Stabilized diphenylmethane diisocyanate-polymethylene polyphenyl isocyanate compositions

ABSTRACT

Liquid reaction product mixtures of diphenylmethane diisocyanates and polymethylene polyphenyl isocyanates resulting from the thermal decomposition of the corresponding carbamates produced by the acid condensation of an N-aryl carbamic acid ester, such as ethylphenylcarbamate, with formaldehyde are storage stabilized against an increase in viscosity and decrease in free NCO content, by incorporating therein an effective amount of a compound having the formula ##STR1## wherein R is hydrogen or an alkyl group having up to 4 carbon atoms, x plus y is equal to 3 and z is an integer of from 0 to 3.

FIELD OF THE INVENTION

The present invention relates to the stabilization of organicisocyanates and more particularly to liquid mixtures of diphenylmethanediisocyanates and the related higher homologs, the polymethylenepolyphenyl isocyanate stabilized against degradation and loss ofvaluable properties with respect to viscosity and free isocyanategroups.

BACKGROUND OF THE INVENTION

Various stabilizer compounds have been proposed for incorporation intoaromatic polyisocyanate compositions including phenols, phosphites, arylhaldies, ureas, thioureas, ureids, acetyls, benzamides, haloacetamides,anilide compounds, tertiary amines and other compounds for color,reactivity and/or storage stability of the isocyanate products, i.e.,the diphenylmethane diisocyanates and polymethylene polyphenylpolyisocyanates, prepared by the phosgenation of the correspondingpolyamines obtained in the acid condensation of aniline andformaldehyde. Such polyisocyanates produced by phosgenation contain freehydrogen chloride and a wide variety of by-products containinghydrolyzable chloride which affect the overall stability.

U.S. Pat. No. 3,660,456 shows, for example, that organic isocyanatesprepared by phosgenation may be stabilized by a variety of differentcompounds and U.S. Pat. No. 3,880,784 shows the use of semiacetals offormaldehyde. Many of the isocyanate stabilizer compositions haveundesirable properties. Some are highly toxic or have obnoxious odors,while others decrease the effectiveness of catalysts used to preparepolyurethane products from polyisocyanates.

It is known that diphenylmethane diisocyanates and polymethylenepolyphenyl polyisocyanates, devoid of the above noted chlorideimpurities, also tend to increase in viscosity and decrease in freeisocyanate content on storage through reaction of the isocyanate groupsto form various polymerics, which process, limits the shelf life of theisocyanates and is undesirable. These diisocyanates and polyisocyanatesare prepared by the thermal decomposition of the correspondingcarbamates in a suitable solvent as shown, for example, in Rosenthal etal, U.S. Pat. No. 3,962,302; the carbamates having resulted from theacid condensation of N-aryl carbamic acid esters with carbonyl compoundssuch as formaldehyde as set forth, for example, in Shawl, U.S. Pat. Nos.4,162,362 and 4,202,986.

SUMMARY OF THE INVENTION

This invention relates to the stabilization of liquid mixtures ofdiphenylmethane diisocyanates and the higher molecular weight homologs,polymethylene polyphenyl isocyanates, against viscosity increase andfree isocyanate loss on storage without undesirable effects on thereactivity of the isocyanate products. More specifically, the presentinvention concerns the stabilization of a liquid reaction productmixture of diphenylmethane diisocyanates and polymethylene polyphenylisocyanates prepared by the thermal decomposition of the correspondingdiphenylmethane dicarbamates and polymethylene polyphenyl carbamatesresulting from the acid catalyzed condensation of an N-aryl carbamicacid ester with formaldehyde.

It is therefore an object of this invention to provide a stabilizedliquid mixture of diphenylmethane diisocyanates and polymethylenepolyphenyl isocyanates, prepared by the thermal disassociation of thecorresponding carbamates, which are substantially free of theabove-mentioned problems and disadvantages. Another object of thisinvention is to provide an improved mixture of the liquiddiphenylmethane diisocyanates and polymethylene polyphenyl isocyanateswhich are substantially stable to viscosity changes and loss of freeisocyanate (NCO) content.

These and other objects and advantages of this invention will becomeapparent from the description of the invention which follows and fromthe claims.

DESCRIPTION OF THE INVENTION

In accordance with the present invention a liquid reaction productmixture of diphenylmethane diisocyanates and polymethylene polyphenylisocyanates, derived from the thermal decomposition in solvent of thecorresponding diphenylmethane dicarbamates and polymethylene polyphenylcarbamates, are stabilized against viscosity changes and loss of freeisocyanate (NCO) content by incorporating into the isocyanate in thecrude or purified form, from about 0.001 to 1.0 percent preferably from0.01 to 0.2 percent by weight of a compound having the general formula##STR2## wherein R is hydrogen or an alkyl group having from 1 to 4carbon atoms, x plus y is equal to 3 and z is an integer of from 0 to 3.

The liquid diphenylmethane diisocyanate-polymethylene polyphenylisocyanate mixtures which may be stabilized according to the inventionare, as indicated hereinabove, prepared by the thermal decomposition ofthe corresponding carbamates dissolved in a suitable solvent as shown,for example, in U.S. Pat. Nos. 3,962,302 and 3,919,279, with thecarbamate being prepared by the acid condensation of an N-aryl carbamicacid ester, such as ethylphenylcarbamate with formaldehyde. Suchprocesses produce liquid diphenylmethane diisocyanate-polymethylenepolyphenyl isocyanate mixtures containing from about 20 to 85 weightpercent diphenylmethane diisocyanate as the 4,4' and 2,4' isomers with aminor amount of the 2,2' isomer, with the balance of the mixture beingthe related higher molecular weight polymethylene polyphenyl isocyanatesand from about 3 to 9 percent by-product impurities such ascarbodiimides, biurets, and ureas which result from the condensation anddecomposition reactions. Of the diphenylmethane dicarbamates in thecarbamate product mixture, the 4,4' isomer to 2,4' isomer will rangefrom about 4:1 to 20:1 as is described for example in U.S. Pat. No.4,230,877.

The stabilizer compounds having the formula hereinabove described whichmay be employed with the liquid diphenylmethanediisocyanate-polymethylene polyphenyl isocyanate mixtures include, forexample, N-(2-hydroxyethyl)chloroacetamide,N-(2-hydroxyethyl)-trichloroacetamide,N-(2-hydroxypropyl)chlorobutyramide,N-(2-hydroxybutyl)trichloropropamide,N-(2-hydroxyethyl)-2,2-dichloroacetamide,N-(2-hydroxyethyl)-N-methyltrichloroacetamide, etc. The stabilizingcompounds are simply mixed with the liquid diphenylmethanediisocyanate-polymethylene polyphenyl isocyanate mixture at anyreasonable temperature preferably ambient temperatures. Standardhandling procedure for the polymeric isocyanates after addition of thestabilizer compound is adequate. The amount of stabilizer employedshould be adjusted to provide adequate stabilization against theundesired degradation effects on storage and is preferably in the rangeof from about 0.01 to about 0.20 percent by weight based on the weightof the liquid isocyanate mixture.

The stabilized isocyanates of the instant invention are valuablestarting materials for the preparation of polyurethanes and for use inreactions and other applications conventional in the art for such liquiddiphenylmethane diisocyanate-polymethylene polyphenyl isocyanatemixtures. The stabilizers of the instant invention do not in any waydetract from the reactivity or other behaviour of the isocyanates.

The following examples are provided to illustrate the invention inaccordance with the principles of this invention, but are not to beconstrued as limiting the invention in any way except as indicated bythe appended claims.

EXAMPLE 1

To a liquid mixture of diphenylmethane diisocyanates and the highermolecular weight homologs polymethylene polyphenyl isocyanates,(prepared by the condensation of ethylphenylcarbamate with formaldehydeas set forth in U.S. Pat. No. 4,162,362 followed by thermaldecomposition of the carbamate to the isocyanate per U.S. Pat. No.3,962,302), was added, as stabilizer, 0.068 percent by weightN-(2-hydroxyethyl)trichloroacetamide prepared by a method outlined inOrganic Syntheses, Collective Volume V, pages 1074-1075. The stabilizedisocyanate mixture was placed in a 25 cc bottle which was purged withnitrogen, capped and sealed as was a control sample of unstabilizedisocyanate. The initial isocyanate (NCO) content of the samples was 30.7with a viscosity of 178 centipoise (cp.) at 25° C. The bottles wereplaced in an oven at 62° C. for 476 hours after which the samples wereremoved and analyzed for viscosity and NCO content. The control sampleshowed a viscosity of 1470 cp. at 25° C. with an NCO content of 28.8percent while the stabilized sample had a viscosity of 264 cp. at 25° C.and an NCO content of 30.4.

EXAMPLES 2 to 8

In Examples 2 to 8, which follow in Table form the procedure of Example1 was repeated employing various stabilizers, amount of stabilizer andconditions with 25 cc. sample bottles of the same 30.7 NCO and 178 cp.viscosity liquid diphenylmethane diisocyanate-polymethylene polyphenylisocyanate mixture of Example 1. Analysis for the NCO content andviscosity of the solutions, including control samples, showing theeffect of the stabilizers are set forth.

                                      TABLE                                       __________________________________________________________________________                                      Viscosity                                   Example              Temp.                                                                             Time     (cp. at                                     No.   Stabilizer (% by Wt.)                                                                        °C.                                                                        (hrs.)                                                                            NCO %                                                                              25° C.)                              __________________________________________________________________________    2     N-(2-hydroxyethyl)trichloro-                                                                 30  1440                                                                              30.5 185                                               acetamide (0)                                                           --    Example 2 Control                                                                            30  1440                                                                              28.9 1635                                        3     N-(2-hydroxypropyl)chloro-                                                                   60  720 30.4 245                                               butramide (.10)                                                         4     N-(2-hydroxybutyl)chloro-                                                                    60  720 30.4 252                                               acetamide (.10)                                                         5     N-(2-hydroxybutyl)trichloro-                                                                 60  720 30.6 226                                               propamide (.20)                                                         --    Example 3,4,5 Control                                                                        60  720 28.3 1560                                        6     N-(2-hydroxybutyl)chloro-                                                                    25  1440                                                                              30.3 180                                               acetamide (.25)                                                         --    Example 6 Control                                                                            25  1440                                                                              28.4 1520                                        7     N-(2-hydroxyethyl)trichloro-                                                                 62  476 30.5 183                                               acetamide (.40)                                                         8     N-(2-hydroxyethyl)trichloro-                                                                 62  476 30.3 286                                               acetamide (.020)                                                        __________________________________________________________________________

We claim:
 1. A method for the storage stabilization of liquiddiphenylmethane diisocyanate-polymethylene polyphenyl isocyanatemixtures derived from the thermal decomposition of the correspondingdiphenylmethane dicarbamates and polymethylene polyphenyl carbamatesprepared by the acid condensation of N-aryl carbamic acid ester withformaldehyde, which comprises incorporating in said liquid isocyanatemixtures from about 0.001 to 1.0 percent by weight of an amide compoundhaving the formula ##STR3## wherein R is hydrogen or an alkyl grouphaving from 1 to 4 carbon atoms, x plus y is equal to 3 and z is aninteger of from 0 to
 3. 2. A method according to claim 1 wherein theamide compound is selected from the group consisting ofN-(2-hydroxyethyl)trichloroacetamide,N-(2-hydroxypropyl)chlorobutramide, N-(2-hydroxybutyl)chloroacetamide,N-(2-hydroxybutyl)trichloropropamide,N-(2-hydroxyethyl)-2,2-dichloroacetamide andN-(2-hydroxyethyl)N-methyltrichloroacetamide.
 3. A method according toclaim 2 wherein the amide is N-(2-hydroxyethyl)trichloroacetamide.
 4. Amethod according to claim 1 wherein the amide compound is employed in anamount of from 0.01 to 0.2 percent by weight.
 5. A process according toclaim 1 wherein the diphenylmethane diisocyanate content of the liquidisocyanate mixture is from about 20 to 85 weight percent.